Abstract:
The important role of mesopores has been investigated in electric double-layer capacitors (EDLCs) operating from 24 °C
down to−40 °C by using two in-house synthesized carbons with hierarchical porosity. These carbons were prepared from
colloidal nanoparticles of SiO2 as the template and d-glucose as the carbon source. A decrease in the average diameter of
the nanoparticles from 12 to 8 nm results in increased surface area and ofers a perfect match between ions of binary mixture
of imidazolium-based fuorinated ionic liquids and the pores of carbon. Short-range graphene layers produced with 8-nm
silica nanoparticles lead to the creation of transport channels which better accommodate ions. We explain these fndings per
coulombic interactions among the ions and between the pore wall and the ionic species under confnement and electrochemical polarization conditions. Further, it is shown that a microporous carbon (another in-house produced rice-husk carbon
SBET=1800 m2
∙g−1) performs better than hierarchical carbons at room temperature; however, thanks to the large fraction
of mesopores, the latter exhibit far higher capacitance down to−40 °C. While the ordering of ions in confnement is more
critical at room temperature and dictated by the micropores, low temperature performance of supercapacitors is determined
by the mesopores that provide channels for facile ion movement and keep the bulk ionic liquid–like properties.